1. Field of the Invention
The present invention relates to a liquid crystal display device in which a disconnection defect occurring in a storage capacitor bus line in a manufacturing process of the liquid crystal display device used as a display device of a personal computer or the like can repaired, and a defect repairing method for the same.
2. Description of the Related Art
A liquid crystal panel of a liquid crystal display device has such a structure that two glass substrates of a TFT substrate on which thin film transistors (TFT) and the like are formed and a CF substrate on which color filters (CF) and the like are formed, are made opposite to each other, liquid crystal is sealed between them, and they are attached to each other.
On the TFT substrate, there are provided a plurality of gate bus lines, a plurality of drain bus lines intersecting with the gate bus lines through an interlayer insulating film, storage capacitor bus lines crossing pixel regions defined by the gate bus lines and the drain bus lines in parallel with the gate bus lines, and extraction lines (lead lines) for connecting the gate bus lines and the drain bus lines respectively to terminal portions for external connection. Incidentally, a TFT of which a drain electrode is connected to the drain bus line is formed in the vicinity of each of intersections of the respective bus lines. A source electrode of the TFT is connected to a pixel electrode disposed in each of the pixel regions.
In the liquid crystal display device, reduction in manufacturing costs is an important problem. For the reduction in costs, first, the improvement in manufacturing yield is intensely desired. One of causes for reducing the manufacturing yield of the liquid crystal display device is a disconnection defect occurring in a wiring pattern such as the storage capacitor bus line formed on the TFT substrate. The disconnection defect is repaired by a laser repair using a laser CVD (Laser Chemical Vapor Deposition) method, or the like.
Here, a conventional defect repairing method for a liquid crystal display device will be described with reference to FIGS. 28 to 30D. FIG. 28 is a plan view showing the defect repairing method for the liquid crystal display device in which a disconnection defect occurs in a storage capacitor bus line 515. As shown in FIG. 28, a plurality of drain bus lines 501 extending in the vertical direction in the drawing are formed on a substrate. Besides, a plurality of gate bus lines 503 indicated by broken lines extending in the horizontal direction in the drawing are formed on the substrate. Pixel regions are formed in regions defined by the drain bus lines 501 and the gate bus lines 503. A TFT 521 is formed in the vicinity of each of intersections of the respective drain bus lines 501 and the respective gate bus lines 503.
A drain electrode 517 of the TFT 521 is extended from the drain bus line 501 shown at the left side in the drawing, and its end portion is formed to be positioned at one end side on a channel protection film 505 formed on the gate bus line 503.
On the other hand, a source electrode 519 is formed to be positioned at the other end side on the channel protection film 505. In such a structure, a region of the gate bus line 503 just under the channel protection film 505 functions as a gate electrode of the TFT 521. Although not shown, a gate insulating film is formed on the gate bus line 503, and an active semiconductor layer constituting a channel is formed thereon.
Besides, storage capacitor bus lines 515 are formed in regions indicated by broken lines crossing substantially the centers of the pixel regions horizontally. A storage capacitor electrode 509 opposite to the storage capacitor bus line 515 through an insulating film is formed on an upper layer of the storage capacitor bus line 515 for each pixel. A pixel electrode 513 made of a transparent electrode is formed on an upper layer of the source electrode 519 and the storage capacitor electrode 509.
The pixel electrode 513 is electrically connected to the source electrode 519 through a contact hole 507 provided in a protection film formed thereunder. Besides, the pixel electrode 513 is electrically connected to the storage capacitor electrode 509 through a contact hole 511.
In the storage capacitor bus line 515 at the upper portion in the drawing, a disconnection defect occurs in one pixel at a disconnection portion 523. First, the drain electrode 517 of the pixel in which the disconnection occurs and the drain bus line 501 are cut away at a cut portion 526. Next, disconnection repairing contact holes 527 in which the storage capacitor bus line 515 is exposed are respectively formed at both end portions of the disconnection of the disconnection defect 523 and in regions where the pixel electrode 513 is not formed on the upper layer. Next, a disconnection repairing conductive film 529 for electrically connecting both the end portions of the disconnection is formed through the disconnection repairing contact holes 527 by a laser CVD method, and the disconnection defect of the storage capacitor bus line 515 is repaired. At this time, the disconnection repairing conductive film 529 is connected with the pixel electrode 513. Besides, in the storage capacitor bus line 515′ at the lower portion in the drawing, a disconnection defect in a wide range occurs at a disconnection portion 525 extending over two pixels. The storage capacitor bus line 515′ in which the disconnection defect occurs at the disconnection portion 525 is repaired similarly to the storage capacitor bus line 515.
The conventional defect repairing method for the liquid crystal display device in which the disconnection defect occurs in the storage capacitor bus line 515, will be described more specifically with reference to FIGS. 29A to 30D. FIGS. 29A to 30D show sections of the vicinity of the storage capacitor bus line 515 taken along line A-A′ of FIG. 28. Incidentally, it is assumed that before the disconnection repairing contact holes 527 shown in FIG. 28 are formed, a disconnection inspection of the storage capacitor bus line 515 is carried out in advance, and as a result of the disconnection inspection, the disconnection portion 523 of the storage capacitor bus line 515 shown in FIG. 28 is found.
First, as shown in FIG. 29A, the storage capacitor bus line 515 is formed on a glass substrate 531. Here, the disconnection defect occurs in the storage capacitor bus line 515 at the disconnection portion 523. Next, an insulating film 533, an amorphous silicon (a-Si) layer 535, and a channel protection film formation layer 537 are formed in this order on the storage capacitor bus line 515. Next, a channel protection film formation layer 537 is patterned so that a channel protection film (not shown) is formed only on a gate electrode (not shown) (FIG. 29B).
Next, as shown in FIG. 29C, an n+a-Si layer 539 and a metal layer 541 are continuously formed on the whole surface. Next, as shown in FIG. 29D, the metal layer 541, the n+a-Si layer 539 and the a-Si layer 535 are patterned by simultaneous etching to form the storage capacitor electrode (intermediate electrode) 509. Next, as shown in FIG. 30A, a protection film 543 is formed on the whole surface of the storage capacitor electrode 509. Next, as shown in FIG. 30B, a transparent conductive film is formed and is patterned, so that the pixel electrode 513 is formed.
Next, the drain electrode 517 of the pixel in which the disconnection defect occurs is cut away at the cut portion 526 and is separated from the drain bus line 501. Next, as shown in FIG. 30C, the disconnection repairing contact holes 527 in which the storage capacitor bus line 515 is exposed are formed at both end portions of the disconnection of the disconnection portion 523 and in regions where the pixel electrode 513 and the storage capacitor electrode 509 are not formed on the upper layer. Next, as shown in FIG. 30D, the disconnection repairing conductive film 529 for electrically connecting both the end portions of the disconnection is formed through the disconnection repairing contact holes 527 on the pixel electrode 513 by using the laser CVD method.
However, when the disconnection defect occurring in the storage capacitor bus line 515 is repaired by using the conventional defect repairing method for the liquid crystal display device as described above, as shown in FIG. 30D, the storage capacitor bus line 515 and the pixel electrode 513 are short-circuited through the disconnection defect repairing conductive film 529. Thus, although it is necessary to provide electrical insulation by cutting away the drain electrode 517 and the drain bus line 501 at the cut portion 526, there arises a problem that the pixel becomes a new point defect. Further, when the disconnection defect in a wide range extending over two or more pixels is repaired, similarly, there arises a problem that those pixels become a connecting point defect.